Morphogenetic differences of secundum atrial septal defects

Morphogenesis and molecular considerations on congenital cardiac septal defects

The primary unseptated heart tube undergoes extensive remodeling including septation at the atrial, atrioventricular, ventricular, and ventriculo-arterial level. Alignment and fusion of the septal components is required to ensure full septation of the heart. Deficiencies lead to septal defects at various levels. Addition of myocardium and mesenchymal tissues from the second heart field (SHF) to the primary heart tube, as well as a population of neural crest cells, provides the necessary cellular players. Surprisingly, the study of the molecular background of these defects does not show a great diversity of responsible transcription factors and downstream gene pathways. Epigenetic modulation and mutations high up in several transcription factor pathways (e.g. NODAL and GATA4) may lead to defects at all levels. Disturbance of modulating pathways, involving primarily the SHF-derived cell populations and the genes expressed therein, results at the arterial pole (e.g. TBX1) in a spectrum of ventricular septal defects located at the level of the outflow tract. At the venous pole (e.g. TBX5), it can explain a variety of atrial septal defects. The various defects can occur as isolated anomalies or within families. In this review developmental, morphological, genetic, as well as epigenetic aspects of septal defects are discussed.

Transcranial Doppler quantification of residual shunt after percutaneous patent foramen ovale closure. Comparison of two devices

BACKGROUND

Recurrent paradoxical embolism after catheter-based closure of right-to-left shunt (RLS) can be related to residual RLS. To improve closure success, we need a better understanding of the anatomic and device-related factors associated with closure efficacy.

METHODS

Patients with cryptogenic neurologic events and severe RLS (Valsalva Spencer transcranial Doppler [TCD] grade 5/5+) who underwent patent foramen ovale (PFO) closure by either central pin (Amplatzer(®) PFO [A-PFO]) or central occluding (Amplatzer(®) SO [A-SO]) devices were evaluated for residual shunt by quantitative TCD evaluation at 3 months. The findings were correlated with atrial septal aneurysm (ASA), device type, and device size.

RESULTS

We closed 628 consecutive patients with either the A-PFO (n = 327) or A-SO (n = 301) device. The frequency of large defects, small defects, and ASA was 12%, 88%, and 44% of cases, respectively. Severe residual shunt was detected in 13% of A-PFO and 7% of A-SO recipients (P = 0.005). This difference was attributable to a much higher frequency of severe residual shunt among patients with large defects closed with the A-PFO compared to the A-SO device (12 out of 29 [41%] vs. 3 out of 42 [7%], respectively; P < 0.001). There was no significant difference in device failure frequency for small defects. The presence of ASA increased the frequency of severe residual shunt compared to those without this feature (36 out of 275 [13%] vs. 28 out of 353 [8%], respectively; P = 0.046) but did not influence device-related differences.

CONCLUSIONS

(1) Both noncentering and central occluding closure devices effectively reduce RLS after PFO closure. (2) Large PFO defects with or without ASA have lower residual shunt grades at 3 months when closed by central occluding devices.

Knockdown of alpha myosin heavy chain disrupts the cytoskeleton and leads to multiple defects during chick cardiogenesis

Atrial septal defects are a common congenital heart defect in humans. Although mutations in different genes are now frequently being described, little is known about the processes and mechanisms behind the early stages of atrial septal development. By utilizing morpholino-induced knockdown in the chick we have analysed the role of alpha myosin heavy chain during early cardiogenesis in a temporal manner. Upon knockdown of alpha myosin heavy chain, three different phenotypes of the atrial septum were observed: (1) the atrial septum failed to initiate, (2) the septum was initiated but was growth restricted, or (3) incorrect specification occurred resulting in multiple septa forming. In addition, at a lower frequency, decreased alpha myosin heavy chain was found to give rise to an abnormally looped heart or an enlarged heart. Staining of the actin cytoskeleton indicated that many of the myofibrils in the knockdown hearts were not as mature as those observed in the controls, suggesting a mechanism for the defects seen. Therefore, these data suggest a role for alpha myosin heavy chain in modelling of the early heart and the range of defects to the atrial septum suggest roles in its initiation, specification and growth during development.

Cardiomyocyte apoptosis in the right auricle of patients with ostium secundum atrial septal defect diseases

Ostium secundum atrial septal defect (osASD) is one of the most commonly occurring cardiac malformations. Although some embryological pathways have been elucidated, the molecular etiologies of ASD are not fully understood. Previous microarray analysis in our laboratory identified differentially expressed genes between osASD and normal right auricular myocardium. Of the 1056 differentially expressed genes, 14 genes were related to apoptosis: eight pro-apoptotic genes were up-regulated and six anti-apoptotic genes were down-regulated in ASD patients. In the current study, we utilized semi-quantitative RT-PCR, electron microscopy, TUNEL and flow cytometry to further understand the role of apoptosis in the atrium of osASD patients. RT-PCR results confirmed differential expression data from previous microarray studies. Additionally, while apoptosis was detected in the right auricular myocardium of all osASD patients, it was absent in controls. These data suggested apoptosis may play an important role in the pathogenesis of osASD or possibly occurs as a consequence of volume overload and hemodynamic changes in right atrium of osASD patients.